1. Field of the Invention
The present invention relates generally to the design of a new type of next-generation memory device, that is, a magnetic random access memory device, that uses voltage-controlled magnetization reversal and giant magnetoresistance phenomena as a method of writing and reading information to and from memory, and performs writing and reading independently of each other and, more particularly, to a nonvolatile, ultra highly-integrated and super power-saving voltage-controlled magnetization reversal writing type magnetic random access memory device and a method of writing and reading information using the magnetic random access memory device, in which voltage is uninterruptedly applied to a lead-zirconate-titanate thin film using two base electrodes composed of positive (+) and negative (−) electrodes, reading and writing are performed independently of each other using two writing lines and two reading lines, and writing is performed by applying voltage to a piezoelectric layer and controlling magnetization in a planar direction or a direction perpendicular to the planar direction using inverse magnetostriction depending on the direction of magnetization of a free ferromagnetic material.
2. Description of the Related Art
Recently, research into next-generation information storage technology has focused on the development of ultra highly-integrated, nonvolatile, low power and ultra high-speed memory, and the Magnetic Random Access Memory (MRAM) technology of a variety of next-generation memory technology is attracting attention as a new technology to satisfy both advantages of the ultra high-integration of Dynamic Random Access Memory (DRAM) and the ultra high-speed of Static Random Access Memory (SRAM).
Up to now, a variety of MRAM technologies based on Magnetic Tunnelling Junction (MJT) have been developed. These technologies are described in U.S. Pat. Nos. 6,518,588, 6,097,625, and 5,640,343.
In accordance with the above-described prior art, the writing of information is performed by changing the direction of magnetization of a magnetic layer using an externally applied magnetic field.
However, in the above-described writing scheme using an externally applied magnetic field, the localization of the magnetic field is not easy, so that there is a fundamental limitation in the development of ultra high-integrated memory.
Furthermore, since existing MRAM technology separates two ferromagnetic thin films from each other, and reads the orientations of relative spins of a magnetic thin film using the magnetoresistance effect caused by tunneling-electrons that are passed through an insulating thin film layer, a pinned layer and a free layer, the thickness of the insulating thin film layer must be about 1 nm.
This acts as a great weak point in the production of MRAM devices because it is difficult to deposit the insulating thin film, which is formed to a constant thickness of 1 nm, on a wafer having a radius of a predetermined number of inches in a production process, and because a precise work is required for the production of MRAM devices.
In writing technology for solving such a problem, the importance of technology that controls magnetization reversal using schemes other than the scheme of externally applying a magnetic field is recently increasing. For this purpose, attempts to control the direction of magnetization by applying current or electrical fields have been conducted.
E. B. Myers experimentally demonstrated current-induced magnetization reversal in a Cu/Co/Cu multilayer thin film structure. This phenomenon is interpreted as resulting from localized exchange interaction between drifting conductive electrons and spins (Myers, E. B., Ralph, D. C., Katine, J. A., Louie, R. N. and Buhrman, R. A., Current Induced Switching. of Domains in Magnetic Multilayer Devices, Science 285, 867-870, 1999).
However, in such a structure, current that is sufficiently small so as not to induce spin switching must be used for the above-described reading current because current for inducing the spin switching is generally used to measure Giant Magnetoresistance (GMR). This can act as a factor that lowers the GMR value.
One attempt to solve the problem involves controlling magnetization reversal using an electric field in a ferromagnetic semiconductor (Chilba, D., Yamanouchi, M., Matsukura, F. and Ohno, H., Electrical Manipulation of Magnetization Reversal in Ferromagnetic Semiconductor, Science 301, 943-945, 2003).
In the case of the above-described method, there is a problem in that a ferromagnetic semiconductor that can be practically used at room temperature has not been developed to date.
Meanwhile, a method of controlling magnetization reversal by applying voltage to a ferromagnetic thin film is described in US Pat. No. 2003/0103371 A1, entitled “Method of Controlling Magnetization Easy Axis in ferromagnetic Films Using Voltage, Ultra High-density, Low Power, Nonvolatile Magnetic Memory Using The Control Method, and Method of Writing Information on The Magnetic Memory.” However, this method uses materials and structures that interfere with the integration of MRAM devices having existing CMOS circuits, so that there is also a problem in that the design is not suitable for ultra high speed MRAM.